add support for POSIX message queues, except mq_notify

src/mq/mq_timedsend.c

@@ -0,0 +1,7 @@
+#include <mqueue.h>
+#include "syscall.h"
+
+int mq_timedsend(mqd_t mqd, const char *msg, size_t len, unsigned prio, const struct timespec *at)
+{
+	return syscall(SYS_mq_timedsend, mqd, msg, len, prio, at);
+}